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Trim tab problem

Discussion in 'Stabs, Tabs & Gyros' started by bobhorn, Aug 6, 2015.

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  1. bobhorn

    bobhorn Member

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    After owning Compromise for three years, trim tabs finally made it to the top of the list. Bennett tabs, reservoir was empty. Filled it, push the down buttons and can hear the pump run but the tabs don't move. No leaks inside the boat. What are common failures? Stuck cylinder, leaking cylinder, bad pump? Major effort to look at the reservoir but I guess that will be my next step to see if the fluid level has gone down.

    Thanks,

    Bob
  2. TeKeela

    TeKeela Member

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    If was empty, I would not immediately blame the pump. It certainly did its job to send the fluid to the path of least resistance.
  3. bobhorn

    bobhorn Member

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    Good point, but after filling it and running both sides up and down several times, the fluid level went down when putting the tabs down, and came back up when retracting the tabs. Had to leave the boat but will do more testing next time. It does seem that the tabs do move. Next time I'll try to get some measurements of the actual motion and then leave them down over night to see if they stay. No telling when the last time they were used.
  4. TeKeela

    TeKeela Member

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    "Filled it, push the down buttons and can hear the pump run but the tabs don't move."

    "running both sides up and down several times, the fluid level went down when putting the tabs down, and came back up when retracting the tabs."
  5. bobhorn

    bobhorn Member

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    The tabs are under the swim platform and it is very difficult to see if they are doing anything. When I first filled the reservoir and ran them I tried to poke at them with a yard stick and it didn't seem that they had moved. Not a very convincing test. Then later I decided to look at the reservoir level and the level going down and back up would indicate the tabs are moving. Next time down there I will remove a drain panel from the swim platform and then at night with a flashlight I should be able to see them move.

    There is obviously a leak since the reservoir was empty, but how much of a leak? Since the fluid returns to the full level with the tabs up it is obviously not a catastrophic leak to where I'm pumping fluid into the water.

    Since I don't know how much or how little POs have used the trim tabs, the fluid might have leaked out over a period of years.

    Will do a over night leak down test next time I'm on the boat.
  6. wdrzal

    wdrzal Senior Member

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    The bypass valve could be stuck open, a spring in that valve could have broken or the bypass pressure set to low.
  7. bobhorn

    bobhorn Member

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    Actually I did a quick check this morning before leaving the boat, just couldn't leave it be, and found that using my "calibrated" yardstick depth gauge, the one trim tab I checked had moved about two inches. Maybe during the first tests there was some build up on the actuator and after repeated attempts it broke free and started to move. This whole thing was kind of haphazard since I was alone and had to do a lot of back and forth to the helm to push the button, to the aft cabin to look at the reservoirs and then up and down to the swim platform.

    Next time I will have the admiral along to push the buttons while I can see what's moving, or not.
  8. NYCAP123

    NYCAP123 Senior Member

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    I strongly suggest you word the request carefully when asking an "admiral" to push your buttons.:rolleyes:

    When in the down position the level should be down, and back at full when up. If there was a leak outside the hull you'd surely see a slick from even a drop leaking. Sounds like they're operating fine. They will lose fluid over time. On small boats I consider checking the fluid level a part of the every cruise engine room check. Where not readily visible then at least twice per season. Some boats really need tabs, some don't. The more you use them the more you check them.
  9. bobhorn

    bobhorn Member

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    Skipping over the button issue, this is exactly what is happening. But I would still feel better to actually get eyeballs on them. As I said before, the leak maybe very minor since I have no idea of prior use and how long did it take for the reservoir to actually empty.
    Not sure this boat will need tabs but I hate having something on board that isn't working. If it's not needed, take it off. We seem to throw something of a wake even at idle speed, maybe I should put down some trim tab even at idle?
  10. olderboater

    olderboater Senior Member

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    One of the best tools we have is a GoPro on a pole. Some have them just on rudimentary long sticks or others on commercially available extensions such as GoPole's. A Reach extends from 14-40'. https://shop.gopole.com/

    This helps in examining under your boat, looking at props, the bottom, etc., and would be very helpful in a situation like the one you're dealing with where you aren't sure the tabs are moving as they should.

    I assume you don't have a trim tab indicator.

    As to putting them down at slow speed, yes. If you have them up, you're basically imitating what a wake boat attempts to do.

    What size boat is "Compromise?" As to you needing trim tabs, I think properly functioning trim tabs will be tremendously beneficial to you in managing ride, performance and adjusting for imbalances such as changes in fuel and water levels.
  11. NYCAP123

    NYCAP123 Senior Member

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    You need thrust to develope lift. Having the tabs down at idle speed should only produce drag, making you burn more fuel. If not down evenly they could also hinder your maneuverability while reversing. If you're throwing too much wake at idle speed you either idle too fast and may need to idle on one motor, or carry too much weight in your stern. Proper use of tabs is to drop them as you come up on plane, then raise them for optimim performance. Next adjust them side to side to level the boat or lean it into the seas. Doing this last step while running will also let you know quick whether they're working or not as you can literally steer you boat with the tabs.

    P.S. If you don't have a gauge, you can figure that full up to full down generally takes about 8 seconds.
  12. bobhorn

    bobhorn Member

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    Compromise, it's a boat but not sailboat, is a 38' twin cabin TT. Twin 225 HP FLs. I have a dinghy on davits on the back, approximately 150 lbs, that may be the wake problem. Not sure about getting it up on plane, don't think my wallet could take it.
    The water in the marina seems to have cleared up and I think I will be able to see them at night using a flashlight. That will give me a chance to time the travel.
  13. NYCAP123

    NYCAP123 Senior Member

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  14. Capt J

    Capt J Senior Member

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    This or the bennett's have 2 solenoids inside the pump. One is for down and the other is for up....Sounds like your down solenoid isn't working.
  15. bobhorn

    bobhorn Member

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    NYCAP123, yes, aft cabin with 150 gal water tank underneath. Don't really see good way to move the cabin though.

    Capt J, I thought the two solenoids were one each for the port and starboard trim tabs.
  16. Capt J

    Capt J Senior Member

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    It might be, it's been several years since I worked on one. I think you're right though. It sounds like either the solenoid is bad, or the connection (small plug) is not right at the pump, or it's not getting voltage back there, or the pump itself is bad. I think the pump reverses to go up or down and the appropriate solenoid opens. Some of the bennett systems are very slow and take probably 15 seconds to go fully down or fully up. I've also seen old hoses collapse and the tabs will go down, but collapse when trying to go up.
  17. bobhorn

    bobhorn Member

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    I did find that the reservoir level goes down when the down button is pushed and the level comes back up when the up button is pushed. So I'm assuming the actuators are moving. Just haven't had the time to get an actual look at what is happening.

    Next time I have help on the boat I will get a closer look at the actual trim tabs while someone pushes the buttons.
  18. NYCAP123

    NYCAP123 Senior Member

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    Once again, you can check it yourself alone when running. Push one tab down. Your boat should turn. Then do the other and you should turn the other way.
  19. NYCAP123

    NYCAP123 Senior Member

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    You can leave the dinghy off, and reduce the amount of water you carry. At 8.345404 lbs. per gallon for the water and the weight of the dinghy, you've got a lot of weight back there. Other than that there's not much you can do about the wake except slow down.
  20. bobhorn

    bobhorn Member

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    No to both, we like to anchor out so we need the dinghy and the water. There's a 75 gal tank in the front that I keep isolated and run off the aft tank until we need more water. That should help. Wake has only been a problem moving through the marina. There's a guy usually working on his boat and I think he may yell at kayakers just for the hell of it.